Grain free dog food IS a marketing gold mine for many dog food manufacturers in response to skin problems from food allergies. It seems logical that wild dogs did not evolve eating grains, its not a food they are adapted to. On the other hand, they did not eat sweet potatoes and peas in the ancient past either, and these are the carbohydrate base of many grain free dog foods.
I spent a fortune over the past years on Earthborn Coastal Catch and Primitive grain free dog food for my dobes. Their skin itching was not, as it turns out, from food allergies but from living in a tropical climate the first four years of their lives. Their 'allergies" went away completely when we moved to a drier climate.
I don’t think that grain free or grain based is the issue. What matters is the quality of the food in the bag. Remember, dog food began as a marketing solution to the costs imposed on multinational corporations by the prohibition against selling moldy, expired, and spoiled vegetables and meat for human consumption. Instead they created dog food and marketed it as something good for your dog. Nothing has changed. In fact, it has gotten worse. Nowadays all those vitamins and supplemental goodies in the dog food, which the manufacturers claim is there to help your dog grow and live a healthier life, are synthetic. Many, like vitamin E, are actually produced from petrochemicals, they are not natural. These synthetic supplements are now coming under suspicion of being carcinogenic, too. And this on top of the carcinogenic properties of moldy grains due to aflatoxin.
A whole industry has been built around perceived differences in dog food quality. For example, look at: Dog Food Analysis - Reviews of kibble https://www.whole-dog-journal.com
You will see that Eukanuba has a very bad reputation among those who evaluate dog food its quality. But I don’t believe the brand of dog food really matters except, perhaps at the extreme end of the quality scale. The real question is, does feeding your dog processed food with a three year shelf life improve or diminish the health of your dog? (Or you, for that matter, in the case of people food). I think we all know the answer to this on an intuitive level, at least. Yet we continue buying processed dog food because it is convenient. We like the reassurance given to us by marketers that we are feeding our dogs healthfully right out of a bag. But is it true?
Personally, going forward, I just replicate the ingredients in the “healthy” dog food in real, fresh form, which will reduce my cost by 60%, and the dog will be happier and I hope healthier. Throw in some bones once in awhile, and all should be good. It’s more work, but isn’t a Dobe worth it?